Under pressure from Australia, Vietnam lifted a sudden ban on veterans who had traveled to the country to mark the 50th anniversary of Australia's most costly battle of the Vietnam War, but officials prevented hundreds from paying their respects at a monument to Australian casualties, Australia's prime minister said Friday.

About 1,500 Australian and New Zealand veterans and their families traveled to Vietnam to commemorate the anniversary on Thursday of the Battle of Long Tan at a cross marking the site where 18 Australian soldiers and hundreds of North Vietnamese and Viet Cong troops died on a rubber plantation on Aug. 18, 1966, Prime Minister Malcolm Turnbull said.

A security officers guard the entrance to the Long Tan Cross in Ba Ria city, Vietnam, on Thursday, Aug. 18, 2016. Australia is making top-level appeals to Vietnam on Wednesday to lift a sudden ban on Australian veterans returning to Vietnam to commemorate

Turnbull said he spoke to his Vietnamese counterpart Nguyen Xuan Phuc for an hour on Wednesday night to persuade the Vietnamese government to lift a ban on all commemorations announced that day.

But officials at the memorial, insisting that only small groups gathered and without uniforms, medals, flags or banners, turned away all but 700 veterans, Turnbull said.

Anniversary lapel pins are worn on the shirt of Australian veteran Keith Payne as he waits on a bus to visit Long Tan Cross in Vung Tau, Vietnam on Thursday, Aug. 18, 2016. Under pressure from top Australian officials, Vietnam on Thursday lifted its sudde

Anniversary lapel pins are worn on the shirt of Australian veteran Keith Payne as he waits on a bus to visit Long Tan Cross in Vung Tau, Vietnam on Thursday, Aug. 18, 2016. Under pressure from top Australian officials, Vietnam on Thursday lifted its sudde

A security officers guard the entrance to the Long Tan Cross in Ba Ria city, Vietnam, on Thursday, Aug. 18, 2016. Australia is making top-level appeals to Vietnam on Wednesday to lift a sudden ban on Australian veterans returning to Vietnam to commemorate

"We're very disappointed that not all of the Australians and their families were able to go to the Long Tan complex and reverently commemorate Vietnam Veterans Day before the Long Tan Cross," Turnbull told Radio 3AW.

"We respect the right of the Vietnamese government to determine what ceremonies and observances are held in their country, but to change the rules literally the day before was very unreasonable," he said.

Veterans' Affairs Minister Dan Tehan earlier said Vietnam had informed Australia of the ban late Tuesday.

Tehan on Wednesday called that "a kick in the guts." He told reporters the veto reflected "deep sensitivities" within Vietnam and was not a response to problems in the bilateral relationship.

The Long Tan anniversary is Australia's official Vietnam Veterans Day and has been commemorated by Australians at the battle scene since 1989.

Turnbull said the rules for next year's commemoration would be agreed with Vietnam "very, very clearly and very publicly so there is absolutely no possibility for any misunderstanding."

In the fighting, a company of 105 Australian soldiers plus three New Zealanders supported by artillery survived a rain-drenched, three-hour battle by driving off wave after wave of attacks by more than 2,000 enemy troops.

On Thursday, hundreds of veterans and their families gathered in the Australian capital to mark the anniversary at the Australian War Memorial.

Australia deployed more than 60,000 military personnel to Vietnam between 1962 and 1973, of whom 521 were killed.